Voice and data signals (“telecommunications signals”) are presently transmitted from a sender to a receiver, e.g., from telephone to telephone, by a transmission network. The network includes many interconnected transmission links for carrying the signals. In some instances, such transmission links are mechanical devices, such as fiber optic cable or twisted pair copper wiring. In other instances, such transmission links may comprise assigned bandwidth of a radio frequency link (i.e., a radio channel).
Transmission links are connected to monitoring systems at various intervals. Each monitoring system typically includes circuitry, known as a “receive framer,” that is part of transmission link monitoring hardware in communication with one or more transmission link(s). For example, an end of a fiber optic cable transmission link may be physically connected to the receive framer, which in many applications is embodied in a printed circuit board. The monitoring system also includes a microprocessor, which performs various tasks, including communication with the receive framers. Such monitoring systems may be located at nodes of a public switched network, at nodes of the Internet, or near an edge of a network, e.g., in a customer's building. Each transmission link may carry numerous transmission channels and numerous transmission links may be connected to a single monitoring system.
Each receive framer of the monitoring system monitors respective transmission links for a change of status or for occurrence of various events (collectively, “events”). For example, the events may include occurrence of an alarm condition, a change in signaling, a change in framer state, or reaching of a bit error counter threshold. Examples of alarm conditions include “loss of frame alignment”, “loss of input”, and “cyclic redundancy check failure” alarms.
When an event occurs on a particular transmission link, data relating to the event (e.g., the source of the event, the new state of the event if it relates to an alarm, or the new value of the event bits if it relates to a change in a signaling state) is received at receiving ports and is typically distributed and stored at various registers of the receive framer.
FIG. 1 is a block diagram of a transmission link monitoring system 20 in accordance with the prior art. This embodiment includes three receive framers 22, 24, 26, each of which is connected to three transmission links, 22a, 22b, 22c, 24a, 24b, 24c, 26a, 26b and 26c. Each receive framer is connected to, or in communication with, a microprocessor 28 of the monitoring system 20. When an event occurs on a transmission link, e.g., 22a, the associated receive framer, e.g., 22, sends an interrupt signal to the microprocessor 28, as shown at A in FIG. 1. The interrupt signal alerts the microprocessor to the existence or occurrence of the event, but does not include any data containing information about or relating to the event. The microprocessor 28, which is typically operating to perform an unrelated task of primary importance, stops performing the primary task and executes interrogation software. Using the software, the microprocessor 28 interrogates the receive framer 22 (as shown at B in FIG. 1) and any related hardware (not shown), if necessary, to determine all of the pertinent event data and address data relating to the event. This data is gathered, for example, by reading all storage locations of all registers and data ports of the receive framer and/or recognizing a port and/or channel number where the event occurred. The microprocessor then assembles the pertinent information into a message and forwards the message to a control system (not shown) for responding to the event. The microprocessor may then return to its primary task.
In typical prior art devices and systems, an interrupt signal has been sent to the microprocessor as the result of every event. Events may occur at random, unpredictable intervals and many events typically occur concurrently during service or as the result of a single equipment failure. As a result, subsequent interrupt signals may be sent to the microprocessor in rapid succession before the microprocessor has finished responding to an earlier interrupt signal. Accordingly, the microprocessor must be equipped with means, such as software, for managing such subsequent interrupt signals. Responding to such subsequent events limits the effectiveness of the microprocessor's performance of its primary task.
In another well-known arrangement, rather than rely upon interrupt signals, the microprocessor polls each receive framer at predetermined intervals, e.g., 10 milliseconds. In such an arrangement, a copy of all data stored in all storage locations and/or registers of all receive framers is temporarily retained and compared against data read during the next polling cycle to identify any changes indicating occurrence of an event. Since the transmission links and associated receive framers may be numerous, this arrangement is particularly burdensome and disruptive to the microprocessor and performance of the primary task. In addition, the time required to respond to an event may be lengthened by the polling interval.
Real-time software is typically required by the prior art devices and systems to enable the microprocessor to check the receive framers and to gather information relating to the event. Such software must be capable of handling numerous interruptions at rapid and/or irregular intervals. Such software is complex, expensive to develop, difficult to test, and prone to malfunction. Additionally, such software makes inefficient use of the microprocessor and limits the effectiveness of the microprocessor's performance of its primary task.
The burdens on the microprocessor and complexity of the software are increasing as the number of transmission links supported by a single receive framer increases. Whereas 1–4 transmission links were recently supported by a single receive framer sharing a single microprocessor, it is now common to support as many as 84 or more transmission links that may contain many thousands of possible event sources with a single integrated circuit and still share one microprocessor.